Abstract

Abstract

Dinitrogen, N2O, and CH4 emissions were measured from a Louisiana flooded rice (Oryza sativa L.) field. Field experiments were conducted on a Crowley silt loam soil (a fine, montmorillonitic, thermic Typic Albaqualf) to determine the effect of fertilizer types and rice plants on evolution of N2, N2O, and CH4 to the atmosphere. Highly labeled (60–74 atom% 15N) urea, (NH4)2SO4, and KNO3 fertilizers were applied into the floodwater at the four- to five-leaf stage to maximize N loss. The direct emissions of N2, N2O, and CH4 were measured at 1, 3, 5, 7, 9, 11, 13, 15, 17, and 21 d after N application. Maximum N2 fluxes from the planted rice plots were 254, 516, and 3 330 g ha−1 d−1 for the urea, (NH4)2SO4, and KNO3 treatments, respectively. Dinitrogen fluxes from the urea, (NH4)2SO4, and KNO3 unplanted plots were 264, 484, and 1 720 g N2 ha−1 d−1, respectively. Nitrous oxide emissions due to fertilizer addition to the soil were low. No increases in N2O emission above control values were recorded for any of the sampling intervals after urea addition. Maximum N2O flux from the (NH4)2SO4 treatments was 4 g ha−1 d−1 on Day 17 and 122 g ha−1 d−1 for the KNO3-treated plots measured on Day 1. Peak CH4 emissions from the planted and unplanted urea-treated plots were 75 and 22 g ha−1 d−1, respectively. Fluxes of CH4 from the (NH4)2SO4 and KNO3 plots were much lower and did not exceed 9 and 18 g ha−1 d−1, respectively, over the 21-d sampling period. This study shows that the type of fertilizer N and presence of rice plants affects the evolution of N2, N2O, and CH4 from a flooded-rice soil to the atmosphere.

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